RFC 3825 Geolocation configuration generator tool

While mobile devices (especially those with a GPS) have made people more aware of geolocation/geotagging, you don’t need a GPS in a device to make it location-aware, nor do you need to resort to IP-based reverse lookups. Location information can be made available on any network that has a DHCP server using the Location Configuration Information DHCP Option defined in RFC 3825. It makes sense: for most wired or wireless networks, the engineer responsible for setting up the DHCP server will know at the least where the server or AP is located, and maybe even static information about the locations of each terminal of a wired port.

The Option has a somewhat unorthodox binary format with non-power-of-2-width fixed point reals. To make generating the DHCP configuration statements easier, I developed a web-based RFC 3825 location configuration generation tool. It’s all client-side and even has a Google Maps preview of the location!

Copy the configuration to your local DHCP server, grab an appropriate geolocation library, and you’re ready to go! The tool generates a DHCP LCI Option for both dnsmasq and ISC’s dhcpd.

The lack of fixed point integers in Javascript made the implementation a little trickier than it would have been in, say, C.

Other lessons: Google Maps is not highly accurate.

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2 Responses to “RFC 3825 Geolocation configuration generator tool”

  1. David Adam says:

    Nifty; I’ve set this on the UCC’s DHCP server.

    One possible upgrade for your tool is DMS mode – our survey-grade data is in degrees/minutes/seconds/fractions of a second, rather than in decimal degrees, and I couldn’t find an online tool that actually worked to generate the conversion.

  2. Dean says:

    Good to hear :)

    I’ve updated the tool to parse DMS notation like: 115 48′ 58.02″ (and some intuitive variants)… Now to start hacking CoreLocation to use the DHCP info instead of relying on Skyhook.

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